Method for determining viscoelastic properties of a biological medium, associated module and device

Abstract

The invention relates to a module for determining viscoelastic properties, referred to as the module, of a moving biological medium of variable thickness, referred to as the medium, which is at least partially enclosed in an elastic biological environment. The module comprises a processing unit arranged to calculate a dispersion curve of the at least one shear wave in the medium, based on data relating to the propagation of at least one shear wave in the medium, and to determine a thickness of the medium and / or the viscoelastic properties of the medium, based on the dispersion curve of the at least one shear wave in the medium and a mode of propagation of the at least one shear wave in the medium.

Description

DESCRIPTION Method for determining the viscoelastic properties of a biological medium, module and associated device D omaine technique

[0001] La présente invention se rapporte au domaine de la caractérisation des properties of organic tissues in motion.

[0002] La présente invention concerne plus précisément la détermination de viscoelastic properties of soft tissues in motion.

[0003] L’invention s’inscrit dans le domaine des techniques de caractérisation non invasive and non-invasive tissues.

[0004] L’invention appartient au domaine de l’imagerie médicale par ultrasons.

[0005] L’invention relève, en particulier, de l’échographie ultrasonore ultrarapide.

[0006] L’invention vise, par exemple, les domaines de la physiologie de l'exercice, the sciences of rehabilitation or even the control of artificial respirators. tat de la technique

[0007] Il est connu de l’état de la technique l’échographie ultrasonore ultrarapide. This type of ultrasound scanner emits ultrasound waves and detects the ultrasound waves reflected by soft and / or elastic biological tissue at a frequency above 1.5 MHz. It allows for the characterization of an individual's soft and / or elastic tissues.

[0008] Néanmoins, les méthodes de l’état de la technique présentent un certainNumerous limitations and shortcomings exist, particularly concerning the accuracy of the determined viscoelastic properties of moving media or media whose thickness varies over time. State-of-the-art methods necessarily introduce a relative error in the estimation of the determined viscoelastic properties of the medium.

[0009] En outre, les méthodes de l’état de la technique requièrent d’utiliser des Ultrasound scanners in B-mode, that is, in anatomical imaging mode, are used to determine the position of the target tissue to be studied. This mode imposes significant hardware constraints, particularly regarding the electronic device and the resources required for data processing.

[0010] De plus, le B-mode des échographes classiques de l’état de l’art est operator dependent.

[0011] Un des tissus d’intérêt dont la caractérisation des propriétés viscoelastic properties still need improvement, particularly the diaphragm.

[0012] Un but de la présente invention est de remédier à au moins un des disadvantages of the state of the art.

[0013] Un autre but de l’invention est de :- to allow a more precise determination of the viscoelastic properties of a soft biological medium, and / or to allow a determination of the viscoelastic properties of a biological medium without using B-mode ultrasound imaging for positioning, and / or to allow a determination of the position of the biological medium within its environment, and / or to allow a determination of the position of the biological medium within its environment without using B-mode ultrasound imaging, and / or to allow a determination of the thickness and / or the variation in thickness of the biological medium. Description of the invention

[0014] À cet effet, il est proposé selon l’invention un procédé de détermination of viscoelastic properties, called process, of a biological medium, preferably soft or elastic, of variable thickness in motion, called medium, at least partially enveloped in an elastic or soft biological environment, called environment.

[0015] Le procédé comprend les étapes consistant à :- to calculate, preferably using a processing unit, preferably the processing unit of the module or device according to the invention, from propagation data of at least one shear wave in the medium, preferably in a given or considered plane of the medium, a dispersion curve of at least one shear wave in the medium, preferably in a given or considered plane of the medium, - to determine, preferably using a processing unit, preferably the processing unit of the module or device according to the invention, a thickness of the medium, preferably determined over a time period corresponding to the propagation of a shear wave in the medium, preferably in a given or considered plane of the medium, and / or the viscoelastic properties of the medium, preferably as a function of or relative to the thickness of the medium,from the dispersion curve of at least one shear wave in the medium and one or more propagation modes of at least one shear wave in the medium.

[0016] Selon l’invention, il peut être entendu par tissus mous : les tendons, les ligaments, muscle tissue, or vascular tissue.

[0017] Selon l’invention, il peut également être entendu par tissus mous, en in particular the biological environment: organs, such as, for example, the liver, kidneys or spleen.

[0018] La propagation d’une onde de cisaillement dans le milieu peut être définie such as the spatial displacement of the disturbance in the medium caused by at least one shear wave.

[0019] Il peut être entendu par au moins une onde : une seule onde ou une onde at a given instant or several waves, or a set of waves, of successive shears (or propagating successively) in the medium.

[0020] De préférence, il est entendu par « données de propagation d’au moinsa shear wave in the medium": the propagation data of at least one shear wave in a given or considered plane of the medium and / or environment, preferably in several given or considered planes, preferably again in several given or considered planes corresponding to several depths of the medium and / or environment.

[0021] De préférence, l’au moins une onde de cisaillement dans le milieu est une acoustic shear wave propagating through the medium.

[0022] Les données de propagation peuvent comprendre :- the propagation speed of at least one shear wave in the medium, preferably in a given or considered plane of the medium and / or the environment, preferably in several given or considered planes, preferably again in several given or considered planes corresponding to several depths of the medium and / or the environment, and / or - the position, preferably the relative position, of the shear wave in the medium, preferably in a given or considered plane of the medium and / or the environment, preferably in several given or considered planes, preferably again in several given or considered planes corresponding to several depths of the medium and / or the environment, as a function of time, and / or - the amplitude of at least one shear wave in the medium, preferably in a given or considered plane of the medium, as a function of time and / or the position, preferably the relative position, of the shear wave in the medium,preferably in a given or considered plane of the medium and / or environment, preferably in several given or considered planes, preferably again in several given or considered planes corresponding to several depths of the medium and / or environment.

[0023] De préférence, le ou les modes de propagation de l’au moins une onde de shear in the medium correspond to or constitute the solution(s) of the propagation equation of a shear wave in the medium.

[0024] Le ou les modes de propagation de l’au moins une onde de cisaillement in the environment can be included in a database containing the propagation mode(s).

[0025] Le ou les modes de propagation de l’au moins une onde de cisaillement in the environment can be calculated by a processing unit, preferably by means of a processing unit, preferably the processing unit of the module or device according to the invention.

[0026] La détermination des propriétés viscoélastiques du milieu à partir du ou Propagation modes of at least one shear wave make it possible to improve the accuracy of the values ​​of the determined properties.

[0027] La détermination des propriétés viscoélastiques du milieu à partir despropagation modes of the propagation mode(s) of at least one shear wave allows the thickness of the medium to be determined.

[0028] La détermination des propriétés viscoélastiques du milieu à partir des propagation modes of the propagation mode(s) of at least one shear wave makes it possible to improve the accuracy of the values ​​of the properties determined and / or to determine the thickness of the medium without using ultrasonic imaging in B-mode.

[0029] Les propriétés viscoélastiques du milieu peuvent comprendre : ^ one or more shear moduli of the medium, preferably parallel or perpendicular to fibers constituting the medium,^ a shear viscosity of the medium, preferably parallel or perpendicular to the fibers constituting the medium,^ one or more nonlinear shear moduli parallel or perpendicular to the fibers constituting the medium,^ an anisotropy factor of shear modulus, shear viscosity, or shear nonlinearity.

[0030] De préférence, l’étape de calcul, de préférence mise en œuvre au moyenof a processing unit, preferably the processing unit of the module or device according to the invention, of the dispersion curve of at least one wave of shear in the medium, from propagation data of at least one shear wave in the medium and / or in the environment, propagating in the medium and / or in the environment according to the determined propagation mode, is implemented by Fourier transformation of the propagation data of said at least one shear wave, propagating in the medium and / or in the environment according to the determined propagation mode, in the spatio-temporal domain.

[0031] Selon le procédé, l’étape de calcul, de préférence mise en œuvre au moyenof a processing unit, preferably the processing unit of the module or device according to the invention, may further include, from propagation data of at least one shear wave, propagating, according to the determined mode of propagation, in the medium and / or in the environment, a Fourier transform of the propagation data of said at least one shear wave, propagating, according to the determined mode of propagation, in the medium and / or in the environment, in the spatial domain and a Fourier transform of the propagation data of said at least one shear wave, propagating, according to the determined mode of propagation, in the medium and / or in the environment, in the temporal domain.Preferably, the dispersion curve of at least one shear wave, propagating in the medium according to the determined mode of propagation, being calculated from the Fourier transforms in the spatial domain and in the time domain.

[0032] De préférence, le mode de propagation de l’au moins une onde de Shear in the medium is a dispersive propagation mode guided by the medium.

[0033] De préférence, il est entendu par mode de propagation dispersif guidé par the medium: the solution to the propagation equations of a shear wave guided by the medium dispersing in the elastic biological environment in which the medium is at least partially enveloped.

[0034] De préférence, l’étape de détermination est mise en œuvre en fonction de or from the shear modulus of the medium, the shear modulus of the environment, the density of the medium and the density of the environment.

[0035] Les modes de propagation de l’au moins une onde de cisaillement dans le media may include or be a function of the shear modulus of the medium, the shear modulus of the environment, the density of the medium and / or the density of the environment.

[0036] La prise en compte de l’environnement, en particulier des paramètres dethe environment, to determine the viscoelastic properties of the medium allows to further improve the accuracy of the values ​​of the properties determined.

[0037] La prise en compte de l’environnement, en particulier des paramètres de the environment, allows to improve the accuracy of the thickness of the medium determined.

[0038] De préférence, les données de propagation de l’au moins une onde de shear in the medium include amplitude(s) and / or displacement data of at least one shear wave in the medium.

[0039] De préférence, les données de propagation de l’au moins une onde de shear and / or the dispersion curve of at least one shear wave are, or correspond to or relate to, those of at least one shear wave in a given or considered plane or section of the medium.

[0040] De préférence, le procédé selon l’invention est mis en œuvre pour several, preferably for each, propagation data of at least one shear wave originating from a given plane or section or considered different from the medium.

[0041] De préférence, le milieu est un organe d’un sujet.

[0042] De préférence, l’au moins une onde de cisaillement est générée par : - a physiological process of the subject, - a voluntary action of the subject, and / or - an external stimulus.

[0043] Un processus physiologique du sujet peut être, à titre d’exemple nonlimiting, the subject's heartbeats, the subject's blood circulation or the subject's borborygmi.

[0044] Une action volontaire du sujet peut être, à titre d’exemple non limitatif, a sound emitted by a subject's voice or a snap of the fingers.

[0045] De préférence, le stimulus externe comprend au moins une onde ultrasound emitted by an ultrafast ultrasound imaging device.

[0046] De préférence, le procédé comprend, en outre, une étape de calcul et / ou determination of propagation data of at least one shear wave from ultrasonic waves reflected and detected by the ultrafast ultrasonic imaging device.

[0047] De préférence, le procédé comprend, en outre, une détermination de la presence of the medium in a plane probed by the ultrafast ultrasound imaging device.

[0048] De préférence, le dispositif d’imagerie ultrasonore ultrarapide est agencé to probe one, in particular a single or unique, given or considered plane or one, in particular a single or unique, given or considered section of the medium at a time.

[0049] L’utilisation des modes de propagation de l’au moins une onde de shear makes it possible to determine the presence of the medium in the, in particular the single or unique, plane or in the, in particular the single or unique, probed section of the medium.

[0050] L’utilisation des modes de propagation de l’au moins une onde deshear makes it possible to determine the presence of the medium in the, in particular the single or unique, plane or in the, in particular the single or unique, probed section of the medium without using ultrasonic imaging in b-mode.

[0051] De préférence, le procédé comprend une détermination de la position du environment based on data detected by said ultrafast ultrasonic imaging device.

[0052] L’utilisation des modes de propagation de l’au moins une onde de Shear combined with consideration of the environment, in particular environmental parameters, makes it possible to determine the position of the medium in its environment.

[0053] L’utilisation des modes de propagation de l’au moins une onde de Shear combined with consideration of the environment, in particular environmental parameters, makes it possible to determine the position of the medium in its environment without using ultrasonic imaging in b-mode.

[0054] De préférence, le milieu est un milieu biologique viscoélastique.

[0055] Il peut être entendu par « position du milieu » : la profondeur du milieu(or of the layer, that is to say the layer formed by the medium) or the depth at which the medium is found, in its environment, or the depth position of the medium (or of the layer, that is to say the layer formed by the medium), in its environment.

[0056] De préférence, le milieu est un diaphragme.

[0057] De préférence, lorsque le milieu est un diaphragme, les données de propagation originates or is that of several successive shear waves, or is data or corresponds to data of several successive shear waves propagating in the medium, and covers a continuous duration or extends over a period of at least one respiratory cycle.

[0058] De préférence, l’étape de détermination comprend, en outre, la determination of a variation in the thickness of the medium over time and / or a variation in the thickness of the medium in space.

[0059] Selon un autre aspect de l’invention, il est proposé un programme computer comprising executable instructions which, when executed by computer, implement the steps of the process according to the invention.

[0060] Le programme d’ordinateur peut être en tout langage informatique, tel that for example in machine language, in C, C++, JAVA, Python, Matlab, etc.

[0061] Selon un autre aspect de l’invention, il est proposé un support lisible par computer comprising instructions which, when executed by a computer, cause the computer to implement the process according to the invention.

[0062] Selon un autre aspect de l’invention, il est proposé un appareil de data processing programmed and / or configured and / or arranged to implement the process according to the invention.

[0063] L’appareil de traitement de données peut être un serveur, un ordinateur, a tablet, a calculator, a processor, a computer chip, programmed to implement the method according to the invention, for example by executing the computer program according to the invention.

[0064] Selon l’invention, il est également proposé un module de détermination viscoelastic properties, called modulus, of a biological medium of variable thickness in motion, called medium, at least partially enveloped in an elastic biological environment.

[0065] De préférence, le module convient et / ou est destiné à et / ou agencé pour be connected, by wire or wireless means, to an ultrasound imaging device, preferably to an ultrafast ultrasound imaging device.

[0066] Le module comprend une unité de traitement agencée pour :- calculate, from propagation data of at least one shear wave in the medium, a dispersion curve of at least one shear wave in the medium, -determine, from the dispersion curve of at least one shear wave in the medium and a propagation mode of at least one shear wave in the medium, a thickness of the medium and / or the viscoelastic properties of the medium.

[0067] De préférence, le module comprend des moyens de communication et / ou a connector arranged to communicate with an ultrafast ultrasound imaging device and to receive propagation data of at least one shear wave in the medium from said ultrafast ultrasound imaging device.

[0068] Il peut être entendu par « communiquer » : transférer, recevoir et / ou to emit data.

[0069] Il peut être entendu par dispositif d’imagerie ultrasonore ultrarapide un High-frequency imaging device. By high frequency, it can be understood as the emission and detection of ultrasonic waves at a frequency greater than or equal to 1.5 MHz, typically greater than or equal to 2 MHz.

[0070] Typiquement, il peut être entendu par haute fréquence, une émission etultrasonic wave detection at a frequency between 1 and 15 MHz, typically a frequency of 5 MHz.

[0071] Typiquement, un temps de propagation d’une onde de cisaillement dans The time between the media and the imaging field is on the order of a few microseconds for soft tissues with high stiffness, and a few tens of microseconds, typically around a hundred microseconds, for soft tissues with low stiffness. Also, given the imaging frequency of ultrafast ultrasound imaging devices (capable of producing 20,000 images or more per second), it is possible to obtain, during the propagation of a shear wave through the medium, propagation data from at least 1010 4 images of the shear wave propagating through the medium.

[0072] A titre d’exemple non limitatif, il peut être entendu par dureté élevée : a hardness close to or on the order of 100 kPa. As a non-limiting example, low hardness can be understood as: a hardness close to or on the order of 10 Pa.

[0073] De préférence, l’unité de traitement du module est agencée pourdetermine: - the presence of the medium in a plane probed by the ultrafast ultrasonic imaging device, and / or - the position of the medium from the data detected by the ultrafast ultrasonic imaging device.

[0074] Selon l’invention, il est également proposé un dispositif d’imagerie ultrafast ultrasonic device, for determining viscoelastic properties of a moving biological medium of variable thickness, called medium, at least partially enveloped in an elastic biological environment, called environment.

[0075] Le dispositif comprend une sonde agencée pour émettre au moins une ultrasonic waves and detecting reflected ultrasonic waves.

[0076] De préférence, le dispositif d’imagerie ultrasonore ultrarapide est agencé to detect ultrasound waves reflected by the medium and the environment.

[0077] Selon une première alternative, le dispositif comprend le module selon the invention.

[0078] Selon la première alternative, le module peut être agencé, en outre, pour calculate and / or determine propagation data of at least one shear wave in the medium from ultrasound waves reflected and detected by said ultrafast ultrasound imaging device.

[0079] Selon une deuxième alternative, le dispositif comprend une unité deprocessing arranged to: - calculate, from propagation data of at least one shear wave in the medium, a dispersion curve of at least one shear wave in the medium, - determine, from the dispersion curve of at least one shear wave in the medium and a propagation mode of at least one shear wave in the medium, a thickness of the medium and / or the viscoelastic properties of the medium.

[0080] De préférence, l’unité de traitement du dispositif est agencée, en outre, to determine: - the presence of the medium in a plane probed by the ultrafast ultrasonic imaging device, and / or - the position of the medium from the data detected by the ultrafast ultrasonic imaging device.

[0081] De préférence, la sonde est agencée, en outre, pour émettre au moins an ultrasonic wave capable of generating at least one shear wave in the medium.

[0082] De préférence, le module de détermination de propriétés viscoélastiquesof the medium, preferably the processing unit of the module for determining the viscoelastic properties of the medium, and / or the device for determining the viscoelastic properties of the medium, preferably the processing unit of the device for determining the viscoelastic properties of the medium, according to the invention, is suitable, preferably is particularly suitable, more preferably is designed, and particularly advantageously is specially designed, for implementing the process of destabilizing molten samples and / or the process of determining the viscoelastic properties of the medium. Also, any characteristic of the device for determining the viscoelastic properties of the medium and / or the device for determining the viscoelastic properties of the medium according to the invention is directly applicable to the process of determining the viscoelastic properties of the medium and vice versa. Brief description of the FIGURES

[0083] L’invention sera mieux comprise à la lecture de la description qui va suivre, given solely by way of non-limiting example and made with reference to the attached drawings on which: - FIGURE 1 is a schematic representation of a three-layer model comprising the medium or soft tissue and its environment, - FIGURE 2 includes two graphs illustrating the dispersion relationship of a shear wave propagating in two distinct biological environments, - FIGURE 3 includes two schematic representations of non-limiting examples of embodiments of the viscoelastic property determination module according to the invention, - FIGURE 4 is a schematic representation of a non-limiting example of an ultrafast ultrasound imaging device for the determination of viscoelastic properties according to the invention.

[0084] Sur les figures et dans la suite de la description, les éléments communs à Several figures retain the same reference. Description of an embodiment

[0085] Les modes de réalisation décrits ci-après étant nullement limitatifs, onmay, in particular, consider variants of the invention comprising only a selection of the described features, isolated from the other described features (even if this selection is isolated within a sentence including these other features), if this selection of features is sufficient to confer a technical advantage or to differentiate the invention from the prior art. prior art. This selection includes at least one feature, preferably functional without structural details, or with only part of the structural details if this part alone is sufficient to confer a technical advantage or to differentiate the invention from the prior art.

[0086] Il est présenté un mode de réalisation non limitatif de l’invention.

[0087] L’invention vise à déterminer les propriétés viscoélastiques d’un milieu of variable thickness over time, whose viscoelastic properties also change over time.

[0088] En particulier, l’invention propose une détermination des propriétés viscoelastic which is non-invasive and painless.

[0089] L’invention concerne la détermination de propriétés viscoélastiques deany type of soft tissue in motion at least partially enveloped in an elastic biological environment.

[0090] A cet effet, il est proposé un procédé de détermination de propriétés viscoelastic properties, referred to as the process, of a moving biological medium of variable thickness, referred to as the medium, at least partially enclosed in an elastic biological environment, referred to as the environment. The process includes the step of calculating, from propagation data of at least one shear wave in the medium, the dispersion curve, equation, or relation of the at least one shear wave in the medium. The dispersion relation provides a relationship between the angular frequency (ω) and the wave vector (k) of the at least one shear wave.

[0091] Le procédé comprend, en outre, une étape consistant à déterminer, à starting from the dispersion curve of at least one shear wave in the medium and a propagation mode of at least one shear wave in the medium, a thickness of the medium and / or the viscoelastic properties of the medium.

[0092] A titre d’exemple non limitatif, l’étape de détermination est mise en œuvredepending on or from the shear modulus of the medium, the shear modulus of the environment, the density of the medium and / or the density of the environment.

[0093] De préférence, la densité, exprimée en kg / m3, des tissus mous selon le In this embodiment, the density is considered to be between 1000 and 1100 kg / m³. 3 Soft tissues are also considered virtually incompressible. Poisson's ratios for soft tissues, depending on the embodiment, are close to 0.5.

[0094] De manière avantageuse, le procédé est mis en œuvre à partir de données propagation of several shear waves in the medium and / or in the environment, preferably a set of shear waves in the medium and / or in the environment, preferably again a set or several successive shear waves in the medium and / or in the environment.

[0095] Selon un mode de réalisation non limitatif ingénieux privilégié, l’au moinsGiven the propagation mode of at least one shear wave in the medium, the inventors considered the shear waves to be guided within the medium. Thus, according to the embodiment, the guidance of the shear waves was expressed using guided wave theory, or Lamb wave theory. It should be noted that other models, derived from or arising from, for example, Maxwell's equations or the telegrapher's equations, could have been used.

[0096] Un avantage direct lié à l’utilisation d’une telle description du guidage desThe shear wave model introduces a correspondence between the viscoelastic properties of two semi-infinite environments surrounding the medium, the viscoelastic properties of the medium, and the thickness of the medium. In other words, according to this consideration, the environment / medium system constitutes a three-layer structure. The three-layer medium is represented in Figure 1. In other words, according to this embodiment, the three-layer structure is composed of viscoelastic media. Thus, according to this embodiment, both the medium and the environment are viscoelastic tissues.

[0097] En référence au milieu tri-couche illustré sur la FIGURE 1, est illustré le biological medium 2 of variable thickness in motion and the elastic biological environment comprising a first layer 1, enveloping, at least in part, the medium 2 and the elastic biological environment comprising a second layer 3, enveloping, at least in part, the medium 2. Layers 1 and 3 may constitute a distinct environment.

[0098] Le coefficient ρ (ρ1, ρ2 et ρ3) représentent la densité (masse volumique)in kg / m3, the coefficients μ (μ1, μ2, μ3) represent the shear modulus (where the first Lamé coefficient) in kPa and λ (λ1, λ2 and λ3) represent the second Lamé coefficient in Pa.

[0099] Il est considéré une structure tri-couche 1, 2, 3 solide semi-infinie. La tri- The layer consists of a plate of thickness h with interfaces (considered rigid) corresponding to two semi-infinite solids with assumed infinite lateral dimensions. Considering an orthonormal coordinate system (Oxz) with θ the normal to the trilayer and θ the direction of propagation of elastic waves, each layer is associated with a density (ρ1, ρ2, and ρ3).

[0100] Ainsi, des vitesses longitudinales VLj et transversales VTj de propagation des Elastic waves propagating in each of the three layers 1, 2, 3 can be considered.

[0101] Autrement dit, le milieu 2, est composé d’une structure élastique formant a plate 2 surrounded by two semi-infinite elastic solids 1, 3, resulting in the generation of fleeing longitudinal and transverse waves. The shear waves arriving from environment 1, from above, (^ ^ ^, ^ ^ ^ ) or coming from environment 3, from below, (^^ ^ ^ The values ​​of the two infinite half-spaces are, and must be, zero according to the chosen model. Each layer j=1,2,3 is viscoelastic and the complex Lamé coefficients can be expressed as: μj = μj + iωηj, where ω corresponds to the angular frequency of the shear wave and ηj corresponds to the shear viscosity in Pa.s.

[0102] Les potentiels scalaires sont recherchés sous la forme d’ondes harmonics, propagating along the x-direction. Therefore, the scalar potentials φj and vectors ψj are expressed according to the following equation 1: The respective normal and transverse displacements in layer j, Ajl and Bjl are the amplitudes of the displacements of layer j along the longitudinal polarization direction of the shear wave, and Ajt and Bjt are the amplitudes of the displacements of layer j=1,2,3 along the transverse polarization direction of the shear wave. x and z are the coordinates in the (Oxz) frame, z being the depth in medium 2 and in the biological environment 1, 3, zj corresponds to the depth of the considered layer j plus or minus the thickness of the biological medium 2, t is the time, k is the wavenumber, and ^ ^^ and ^ ^^ correspond respectively to the wavenumber of the shear wave along the longitudinal direction and to the wavenumber of the shear wave along the vertical direction.

[0103] Un axe normal correspond à un axe parallèle à ou confondu avec l’axe z,For example, normal movements are movements along a normal axis, that is, along an axis perpendicular to the biological environment 2. A transverse axis corresponds to an axis parallel to or coinciding with the x-axis; for example, transverse movements are movements along a transverse axis, that is, along an axis included in or coinciding with the plane in which the biological environment 2 extends. A longitudinal axis corresponds to an axis parallel to or coinciding with the y-axis (perpendicular to the x and z axes); for example, longitudinal movements are movements along a longitudinal axis, that is, along an axis included in or coinciding with the plane in which the biological environment 2 extends.

[0104] Les solutions associées aux amplitudes ^^^, ^^^, ^^^ et ^^^ ne sont pas physically admissible because they diverge in depth. Waves arriving from above (^ ^ ^, or from the bottom (^ ^ ^, ^ ^ ^ ) must therefore be considered as null.

[0105] L’idée est de chercher des solutions représentant des ondes se propageantparallel to the interfaces or surface of the medium 2 which corresponds to solutions describing evanescent waves along the z direction.

[0106] D’ici, il est possible d’exprimer un champ de déplacement and ^^^^^^^⃗ ), after Helmholtz decomposition (that is, by expressing: ^^^ = ^^^^(^^) and ^^^ = ^^^(^^)). The expressions for the constraints, denoted ^^^^ and ^^^^, as functions of the scalar potentials φj and vectors ψj can be expressed according to the following equation (2): equation (2).

[0107] En considérant que les conditions aux frontières permettent la continuité normal and tangential constraints and the continuity of normal and tangential displacements at the interfaces in z = z ±h, we obtain a system of eight equations and eight unknowns denoted (^^^, ^^^, ^^^, ^^^, ^^^, ^^^, ^^^, ^^^).

[0108] D’ici, il est possible d’obtenir les expressions des déplacements normauxand transverse stresses in z = z ±(h^2) as well as the expressions for the normal and transverse stresses. From these expressions, it is possible to draw up the transcendental equation, denoted MU, of a semi-infinite solid three-layer structure which can be represented in 8 x 8 matrix form according to the following equation (3): , with M the determinant of the matrix ^^ corresponds to the amplitudes of the displacement field.

[0109] Enfin, pour obtenir les courbes de dispersion (c’est-à-dire la relation entre Given the angular frequency (ω) and wave vector (k) of the shear waves, it suffices to search for values ​​for which the determinant is zero (i.e., M = 0) using, for example, the Newton-Raphson, bisection, or Muller method. Solving the dispersion equation allows us to obtain the pairs (ω, k).

[0110] Les couches 1 et 3, c’est-à-dire l’environnement biologique élastique dansThe mode that wraps around the middle can be different. In this case, it is not possible to divide M into two submatrices to separate the symmetric modes from the antisymmetric modes. However, when the 1, 2, 3 trilayer is asymmetric, it can be observed that the modes of the same family never intersect. Therefore, this will not pose a problem when searching for a branch (mode) using a zero-finding algorithm (Müller type or similar).

[0111] Si le solide semi-infini 1 est identique au solide semi-infini 3, c’est-à-dire that the medium 2 is enveloped within the same biological environment 1, 3, then it is possible to divide M into two sub-matrices thus allowing to separate the family of symmetric modes S from the antisymmetric modes A. We will have A1L = A3L, B1T = B3T, A1T = −A3T, B1L = −B3L, and A2T = B2L = 0 for the symmetric modes S, and similarly, we will have A1L = −A3L, B1T = −B3T, A1T = A3T, B1L = B3L, and A2L = B2T = 0 for the antisymmetric modes A.

[0112] Ces deux sous-matrices sont quasi-similaires puisqu’il suffirait d’ajoutera factor, denoted α, in the cosines and sines of the matrix M. From here, for α = 0 we obtain the submatrix of symmetric modes and for α = π / 2 the antisymmetric modes.

[0113] Aussi, il est important de noter que l’invention n’est pas limitée au mode of particular realization based on the guided wave model as described above but may be realized by means of any model or calculation allowing to establish or including a solution of the equation (therefore at least one mode of propagation) of a shear wave propagating, at least partially, in a biological medium 2 and in a biological environment 1,3, at least partially enveloping said biological medium 2.

[0114] En outre, le modèle ou calcul (c’est-à-dire la solution de l’équation, ou l’au less a mode of propagation, of a shear wave propagating in the medium includes or is a function of the thickness of the medium and of physico-chemical parameters (viscosity, density…) and / or mechanical parameters (Young’s modulus, shear modulus, Poisson’s ratio…) depending on the medium.

[0115] Les données de propagation de l’onde de cisaillement dans le milieu et / ouin the environment, referred to as propagation data in the rest of the description, include or are a function of the depth of the shear wave in the medium (and possibly in the environment). The propagation data consist of, include, correspond to, or are proportional to the propagation speed of at least one shear wave (in medium 2, or in medium 2 and environment 1, 3) and / or the position, or the change in position as a function of time, of the shear wave (in medium 2, or in medium 2 and environment 1, 3) and / or the amplitude, or the change in amplitude, of at least one shear wave (in medium 2, or in medium 2 and environment 1, 3) and / or any other parameter, characteristic or indicator representative or function of the propagation of the shear wave, preferably as a function of time, (in medium 2, or in medium 2 and environment 1, 3).

[0116] Selon l’invention, il est avantageux que les données de propagation include shear wave propagation data in medium 2 and in environment 1, 3.

[0117] Ainsi, à partir du modèle ou calcul et des données de propagation de l’onde of shear, it is established, calculated, determined or chosen (for example in a database) the equation or formula of the mode of propagation of the shear wave in the medium.

[0118] Le procédé peut comprendre une étape d’obtention des données de propagation of the shear wave and / or in the environment.

[0119] Les données de propagation de l’onde de cisaillement dans le milieu et / ou Data is stored in the environment. Therefore, the process can be implemented without a propagation data acquisition step. This allows for the systematic or static study or comparison of the viscoelastic properties of a biological medium based on available (previously acquired) data.

[0120] Le procédé comprend, en outre, l’étape de calcul, à partir de données de propagation of the shear wave in the medium and at least one mode of propagation of the shear wave in the medium, the calculation of the dispersion curve of at least one shear wave in the medium.

[0121] Selon le mode de réalisation, le calcul de la courbe de dispersion de l’ondeshear in the medium is implemented by Fourier transformation, in the spatio-temporal domain, of the propagation data of the shear wave propagating in the medium according to the determined propagation mode.

[0122] En référence à la FIGURE 2, il est illustré des exemples de courbes de dispersions obtained in the case of a soft plate immersed in a liquid, water according to the examples, or charged on one side by water and on the other by a soft elastic solid.

[0123] Le graphique de gauche de la FIGURE 2 illustre la courbe de dispersionFor a soft plate immersed in medium 2, shear waves propagate through medium 2 (according to the determined principal propagation mode), with longitudinal velocities VLj and transverse VTj of elastic wave propagation of 1500 m / s and 5 m / s respectively (corresponding to typical velocities of viscoelastic biological media). Medium 2 has a thickness of 3.6 mm according to the embodiment. The soft plate 2 is completely immersed in water 1, 3, which has longitudinal velocities VLj and transverse VTj of elastic wave propagation (i.e., shear wave propagation data in the medium) of 1500 m / s and 0 m / s respectively.The points correspond to the dispersion curves calculated by spatio-temporal analysis, by Fourier transformation according to the realization mode, of the shear waves propagating in medium 2 (according to the principal propagation mode determined) (corresponding to the solution of the transcendental equation).

[0124] Le graphique de droite de la FIGURE 2 illustre la courbe de dispersion pourA soft plate exhibiting longitudinal (VL2) and transverse (VT2) shear wave propagation velocities of 1500 m / s and 2 m / s, respectively (corresponding to velocities typical of viscoelastic biological media). Medium 2 has a thickness of 3.6 mm according to the embodiment. The soft plate 2 is half-enclosed in water 1 on one side (with VL1 and VT1 of 1500 m / s and 5 m / s) and half-enclosed in a soft solid 3 on the other side (with VL3 and VT3 of 1500 m / s and 15 m / s). The points correspond to the dispersion curves calculated by spatio-temporal analysis, by Fourier transformation according to the realization mode, of the shear waves propagating in the medium 2 (according to the principal propagation mode determined) (corresponding to the solution of the transcendental equation).

[0125] Selon un mode de réalisation particulièrement avantageux mais nonAccording to the limitation of the invention, the propagation data of at least one shear wave in medium 2 and / or in environment 1, 3 originate from or are derived from an ultrafast ultrasound imaging device. The propagation data may be stored digital data or data acquired in real time and processed in real time, according to the invention.

[0126] En référence à la FIGURE 3, il est également proposé, selon l’invention,A module 4 for determining the viscoelastic properties of a moving biological medium 2 of variable thickness, referred to as medium 2, at least partially enveloped in an elastic biological environment 1, 3. Module 4 comprises a processing unit arranged and / or configured and / or programmed to implement the method according to the invention. The schematic representation on the left of Figure 3 illustrates Module 4 according to the embodiment, and the schematic representation on the right of Figure 3 shows the module connected by wire to an external ultrafast ultrasound imaging device 5.

[0127] De manière avantageuse, le module 4 comprend des moyens de communication / reception with (e.g. wireless means of communication via radio waves) and / or a connector arranged to communicate / receive data from an external or remote device 5.

[0128] Les moyens de connexion du module 4 sont aptes et / ou agencés pourto communicate and / or transmit and / or receive data from the external device 5 or remote device 5. According to a non-limiting advantageous embodiment, the external device 5 or remote device 5 is an ultrafast ultrasound imaging device 5. The propagation data of at least one shear wave in the medium 2 originates from, or is provided by, said ultrafast ultrasound imaging device 5.

[0129] Selon un mode de réalisation envisagé, le module 4 peut comprendre une Ultrasonic probe 6 arranged to emit and detect ultrasound reflected by the medium and / or environment. Preferably, in this case, module 4 is arranged to execute instructions from an ultrafast ultrasound imaging device 5 enabling the emission and reception of ultrasound waves.

[0130] De manière avantageuse, le module 4 et / ou le procédé, est agencé pourto determine, by implementation of the process, the position of the and / or locate the (or confirm or detect the presence of the) biological medium 2 in the area probed (i.e. in one or more planes of) the area probed by the ultrafast ultrasonic imaging device 5. Indeed, the determination or selection of the shear wave propagation equation, from the propagation data, allows the discrimination (or identification) of the medium 2 and the environment 1, 3.

[0131] En référence à la FIGURE 4, il est présenté un dispositif d’imagerie ultrafast ultrasonic 7, referred to as device 7, for determining viscoelastic properties according to the invention.

[0132] Le dispositif 7 est agencé et / configuré et / ou programmé pour mettre en implements the process according to the invention.

[0133] Le dispositif 7 comprend une ou des sonde(s) 8 agencée(s) pour émettre ultrasonic waves and detect reflected ultrasonic waves (by the medium and / or by the environment).

[0134] Alternativement, le dispositif 7 peut être défini comme comprenant le module 4 according to the invention. In this case, the device 7 can be defined as the external 5 or remote 5 ultrafast ultrasound imaging device 5.

[0135] Selon l’invention, de manière avantageuse, l’au moins une onde deshear propagating in medium 2 is generated by a non-therapeutic process or stimulus.

[0136] Le stimulus (non thérapeutique) peut être un processus physiologique non provoked (the subject's breathing, the subject's heartbeat, the subject's blood circulation or the subject's borborygmi).

[0137] Le stimulus (non thérapeutique) peut être une action volontaire du sujet, By way of non-limiting example, a sound emitted by the voice of a subject or a snap of the fingers or a voluntary action of the subject or expectoration.

[0138] , Le stimulus (non thérapeutique) peut être un stimulus externe, par example an ultrasound wave (preferably emitted by an ultrafast ultrasound imaging ultrasound scanner).

[0139] Le stimulus (non thérapeutique) peut être un stimulus externe, par For example, electrical and / or magnetic stimulation. Electrical and / or magnetic stimulation can be performed on the nervous system by: - ​​transcranial stimulation, and / or - cervico-medullary stimulation, and / or - stimulation of the phrenic roots, and / or - stimulation of one or two of the main trunks of the phrenic nerve, and / or - stimulation of the diaphragm itself.

[0140] Les sondes ultrasons sont connues de l’homme du métier. La sondeultrasound 6 (of module 4), ultrasound probe 8 (of device 7) or probe 9 of remote ultrafast ultrasound imaging device 5 may include a set of sensors, for example piezoelectric, suitable and / or arranged to emit ultrasound and to capture / detect ultrasound echoes from the probed area 2 and suitable for ultrafast ultrasound imaging.

[0141] Selon un exemple de réalisation avantageuse mais non limitative de the invention, at least one shear wave is generated in the medium 2 by one / of the ultrasonic wave(s) emitted by the ultrasonic probe 6, 8 or 9 (of the module 4, of the device 7 or remote ultrafast ultrasonic imaging device 5).

[0142] Ce mode de réalisation est avantageux car les données de propagation de at least one shear wave in medium 2 (and in environment 1,3) are obtained or acquired, in real time, by module 4, by device 7 or by remote device 5.

[0143] Dans ce cas, les données de propagation de l’ondes de cisaillementcan be considered as the raw data acquired by module 4, device 7 or remote device 5. Alternatively, the shear wave propagation data can be determined or calculated from the raw data acquired or from the ultrasound images.

[0144] De manière préférée, l’épaisseur du milieu 2 et les propriétés viscoelastic properties of medium 2 are determined from the propagation data of several successive shear waves.

[0145] Selon le mode de réalisation non limitatif, le milieu 2 est le diaphragme 2. This organ typically illustrates a medium whose thickness is constantly modified over time and whose viscoelastic properties also change over time, particularly during the respiratory cycle.

[0146] Selon le mode de réalisation présenté, la détermination des propriétés Viscoelastic diaphragms allow for the evaluation of diaphragmatic function during respiratory tasks. Diaphragmatic function can be comprised of or characterized by several parameters or indicators.

[0147] A titre d’exemples non limitatifs, la fonction diaphragmatique peutunderstand contractility and / or diaphragmatic pressure and / or diaphragmatic function and / or diaphragmatic effort and / or diaphragmatic work and / or nerve conduction velocity and / or identification of the spatial organization of the muscle fascicle(s).

[0148] L’homme du métier saura transposer et / ou adapter les paramètres ou indicators of the diaphragm, or of the diaphragmatic function, to other soft tissues according to the invention and may also complement the viscoelastic properties of other soft tissues with other parameters specific to each soft tissue considered.

[0149] L’idée présente de l’invention consiste donc à utiliser l’échographieUltrafast shear wave elastography, coupled with the prior generation of shear waves by ultrasonic radiation pressure, is used to quantify the viscoelastic properties of the diaphragm during ventilation. As described in detail above, the shear waves can also be generated by alternative means, such as one or more external vibrators, the body's natural shear waves (heartbeat, blood circulation, respiration), or the voice. Due to the geometry of the diaphragm in the intercostal imaging zone, a plate of finite thickness (from 500 μm to 10 mm) surrounded by two distinct semi-infinite media (the liver 1 and the intercostal muscle 3), the shear waves propagate in a dispersive and guided manner in the diaphragm 2. Thus the model described according to the embodiment (Guided wave theory or Lamb waves) applies to the tri-layer liver 1, diaphragm 2 and intercostal muscles 3.The guidance of these waves then depends on the viscoelastic properties of two semi-infinite media surrounding the plate (here the diaphragm), the viscoelastic properties of the diaphragm 2 and its thickness. In other words, according to the embodiment, the environment consists of two viscoelastic media or tissues, namely the liver 1 and the intercostal muscles 3.

[0150] Toutefois, l’invention n’est pas limitée au diaphragme. Le milieu peut can also be, for example: - the abdominal walls, for example: subcutaneous fat, abdominals and / or connective tissues (the viscera), and / or - the quadriceps, for example: subcutaneous fat, superficial skeletal muscles and / or deep muscles, and / or - the pelvic floor, for example: connective tissues, the puborectalis muscle and / or the levator ani muscle, and / or - the respiratory muscles, for example: subcutaneous fat, the sternocleidomastoid muscles and / or the scalene muscles.

[0151] Il est également proposé un programme d’ordinateur comprenant desexecutable instructions which, when executed by a computer, implement all or part (but at least some) of the steps of the process according to the invention. In particular, the computer program can be executed or implemented by module 4, by a device 7 and / or by a remote device 5 according to the invention.

[0152] Il est également proposé un support lisible par ordinateur comprenant des instructions which, when executed by a computer, cause the computer to implement the process according to the invention. In particular, the readable medium can be executed or implemented by module 4, by a device 7 and / or by a remote device 5 according to the invention.

[0153] Il est également proposé un appareil de traitement de donnéesprogrammed and / or configured and / or arranged to implement the method according to the invention. In particular, the data processing device may be a component or element of module 4, a device 7, and / or a remote device 5 according to the invention. By way of example, the data processing device may be a processing unit or a computing unit, such as a microprocessor.

[0154] Bien sûr, l’invention n’est pas limitée aux exemples qui viennent d’être described and numerous modifications can be made to these examples without departing from the scope of the invention.

[0155] En particulier toutes les variantes et tous les modes de réalisation décrits are combinable with each other if there are no technical obstacles to this combination.

[0156] Ainsi, dans des variantes combinables entre elles des modes de réalisationpreviously described: - the process includes a step of determining and / or the processing unit is arranged to determine:^ the presence of medium 2 in a plane probed by the ultrasonic waves emitted by the probe 6, 8 or 9; indeed, the equation or formula of the mode of propagation of the shear wave in the medium (corresponding to the solution of the transcendental equation) is a function of the thickness of the medium and the position of the waves in the medium 2 and in the environment 1, 3, and / or ^the position of the medium 2 from the data detected by the probe 6, 8 or 9;Indeed, the equation or formula of the propagation mode of the shear wave in the medium (corresponding to the solution of the transcendental equation) is a function of the thickness of the medium and the position of the waves in the medium 2 and in the environment 1, 3, - the propagation data of at least one shear wave and / or the dispersion curve of at least one shear wave (preferably in the medium 2, or in the medium 2 and in the environment 1, 3) are those of the at least one shear wave in a given or considered plane or section of the medium 2, or of the medium 2 and the environment 1, 3, and / or - the process further includes, (or the determination step further includes) the determination of a variation in the thickness of the medium 2 over time.

Claims

CLAIMS 1. A module for determining the viscoelastic properties, referred to as the module, of a biological medium of variable thickness in motion, referred to as the medium, at least partially enveloped in an elastic biological environment, said module comprises a processing unit arranged to: - calculate, from propagation data of at least one shear wave in the medium, a dispersion curve of at least one shear wave in the medium, - determine, from the dispersion curve of at least one shear wave in the medium and a propagation mode of at least one shear wave in the medium, a thickness of the medium and / or the viscoelastic properties of the medium. 2.Module according to the preceding claim, comprising communication means and / or a connector arranged to communicate with an ultrafast ultrasonic imaging device and to receive propagation data of at least one shear wave in the medium from said ultrafast ultrasonic imaging device.

3. Module according to the preceding claim, wherein the processing unit is arranged to determine: - the presence of the medium in a plane probed by the ultrafast ultrasonic imaging device, and / or - the position of the medium from the data detected by the ultrafast ultrasonic imaging device. 4.Ultrafast ultrasonic imaging device, said device, for determining viscoelastic properties of a moving biological medium of variable thickness, said medium, at least partially enveloped in an elastic biological environment, said environment, said device comprises: - a probe arranged to emit at least one ultrasonic wave and detect reflected ultrasonic waves, and - the module according to any one of claims 1 to 3; said module being further arranged to calculate and / or determine propagation data of at least one shear wave in the medium from. of reflected and detected ultrasonic waves by said ultrafast ultrasonic imaging device, or - a processing unit arranged to:^ calculate, from propagation data of at least one shear wave in the medium, a dispersion curve of at least one shear wave in the medium, ^ determine, from the dispersion curve of at least one shear wave in the medium and a propagation mode of at least one shear wave in the medium, a thickness of the medium and / or the viscoelastic properties of the medium.

5. Ultrafast ultrasonic imaging device according to the preceding claim, wherein the processing unit of the device is further arranged to determine: - the presence of the medium in a plane probed by the ultrafast ultrasonic imaging device, and / or - the position of the medium from the data detected by the ultrafast ultrasonic imaging device. 6.Ultrafast ultrasonic imaging device according to claim 4 or 5, wherein the probe is further arranged to emit at least one ultrasonic wave capable of generating at least one shear wave in the medium.

7. Method for determining the viscoelastic properties, said method, of a biological medium of variable thickness in motion, said medium, at least partially enveloped in an elastic biological environment, said environment, said method comprising the steps of: - calculating, from propagation data of at least one shear wave in the medium, a dispersion curve of at least one shear wave in the medium, - determining, from the dispersion curve of at least one shear wave in the medium and a propagation mode of at least one shear wave in the medium, a thickness of the medium and / or the viscoelastic properties of the medium. 8.Method according to the preceding claim, wherein the step of calculating the dispersion curve of at least one shear wave in the medium, from propagation data of at least one shear wave in the medium,. propagating in the medium according to the determined propagation mode, is implemented by Fourier transform of the propagation data of said at least one shear wave in the medium, propagating in the medium according to the determined propagation mode, in the space-time domain.

9. Method according to claim 7 or 8, wherein the propagation mode of the at least one shear wave in the medium is a dispersive propagation mode guided by the medium.

10. Method according to any one of claims 7 to 9, wherein the propagation data of the at least one shear wave in the medium include amplitude data and / or displacement data of the at least one shear wave in the medium. 11.A method according to any one of claims 7 to 10, wherein the propagation data of at least one shear wave and the dispersion curve of at least one shear wave are those of at least one shear wave in a given or considered plane or section of the medium.

12. A method according to any one of claims 7 to 11, wherein the medium is an organ of a subject and the at least one shear wave is generated by: - ​​a physiological process of the subject, - a voluntary action of the subject, and / or - an external stimulus. 13.A method according to the preceding claim, wherein the external stimulus comprises at least one ultrasonic wave emitted by an ultrafast ultrasonic imaging device; the method further comprises a step of calculating and / or determining the propagation data of at least one shear wave from ultrasonic waves reflected and detected by said ultrafast ultrasonic imaging device.

14. A method according to the preceding claim, further comprising determining the presence of the medium in a plane probed by the ultrafast ultrasonic imaging device.

15. A method according to claim 13 or 14, further comprising determining the position of the medium in the environment from the data detected by said ultrafast ultrasonic imaging device.

16. A method according to any one of claims 7 to 15, wherein the medium is a diaphragm.

17. A method according to the preceding claim, wherein the propagation data are derived from several successive shear waves and cover a continuous duration or extend over a period of at least one respiratory cycle.

18. A method according to the preceding claim, wherein the determination step further comprises determining a variation in the thickness of the medium over time.

19. A computer program comprising executable instructions which, when executed by a computer, implement the steps of the method according to any one of claims 7 to 18.

20. A computer-readable medium comprising instructions which, when executed by a computer, cause the computer to implement the method according to any one of claims 7 to 18. 21.Data processing apparatus programmed and / or configured and / or arranged to implement the process of any one of claims 7 to 18.

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